The 864th Engineer Battalion is a combat engineer battalion of the United States Army based at Joint Base Lewis-McChord, Washington. The battalion is a subordinate unit of 555th Engineer Brigade.

The battalion was the first U.S. engineer battalion-size unit in Vietnam and responsible for port transportation and support facilities construction. As more engineer battalions were assigned to Vietnam, the unit was assigned missions of base camp construction and line of communication construction and maintenance. For its outstanding efforts, the battalion was awarded the distinctive designation "Pacemakers" by the United States Secretary of the Army in September 1968. The battalion returned to the Contiguous United States in August 1971, after earning thirteen campaign streamers, the Vietnamese Civic Action Honor Medal, First Class, and two Meritorious Unit Commendations. In the Contiguous United States, the battalion was assigned to Fort Lewis, Washington.